The present invention relates generally to a riveting machine attachment for indexing and supporting a part to be riveted to a workpiece in an automatic riveting machine and, more specifically, to an attachment for indexing and supporting a nutplate during installation of the nutplate on the workpiece.
Automatic riveting machines, such as those manufactured by ITC Automation ("ITC") of Dayton, Ohio can perform the repetitive steps of drilling one or two holes in a workpiece, feeding one or two solid rivets to the rivet installation head, and installing the rivets in the holes. In the ITC machine, the riveting head and the drilling head are mounted on a reciprocating shuttle, which alternately moves the riveting head and the drilling head to a "Work" position at a point above the workpiece upper surface where the rivets are to be installed.
In each fastening cycle, one or two solid rivets are automatically injected into the riveting head rivet support fingers through a feed tube at a "Load" position. The rivets are held in the support fingers with the rivet heads in contact with the riveting head upper anvil and the rivet tails extending downward. At the Work position, the workpiece upper surface is in contact with an upper pressure foot and the workpiece lower surface is in contact with a lower anvil clamping sleeve. The lower anvil tool is mounted on the riveting machine lower ram, which is adjusted to clamp the workpiece between the upper pressure foot and the lower anvil tool. The drilling head, then at the Work position, descends through an opening in the upper pressure foot and drills a hole in the workpiece. The shuttle then moves the riveting head to the Work position, moving the drilling head out of the way. The riveting head lowers the rivet stem into the hole. Next, the riveting machine lower ram driving pin moves upward through an opening in the lower anvil clamping sleeve to upset the rivet tail, thereby forming the "bucktail" that secures the rivet to the workpiece. The lower ram driver pin then retracts downward and the shuttle moves the drilling head into position to begin the next fastening cycle.
Engineering specifications often require nutplates to be riveted to a workpiece. A nutplate is a well-known part that has a threaded barrel extending therefrom for receiving a threaded shaft or bolt, and one or more holes through which rivets are inserted for fastening the nutplate to a workpiece. Nutplates are commonly manually riveted to a workpiece because of the lack of a suitable automatic nutplate installation attachment for most automatic riveting machines. However, ITC Automation has produced and sold a nutplate fastening device that can be attached to its automatic riveting machines.
Although the ITC attachment increases nutplate installation speed, its use is restricted to substantially flat workpieces. Nutplates are delivered automatically from a vibratory bowl feeder and are received in a "catching chamber" via a feed tube. The catching chamber and attached feed tube form a wide and bulky structure that interferes with workpieces having curved surfaces, or workpieces having perturbations or additional parts extending from the workpiece lower surface.
Furthermore, the ITC attachment produces an unacceptably high number of out-of-tolerance assemblies. After the drilling operation, the ITC attachment aligns the nutplate rivet holes with the holes in the workpiece at an intermediate location, between the Load position and the Work position, and then installs the rivets. The drilling operation often leaves exit burrs around the holes, which prevent the nutplate from lying flush on the workpiece surface during riveting. Nutplates standing off from the workpiece surface often exceed allowable manufacturing tolerances and must be removed and replaced.
Practitioners in the art of automatic fastening have long known that numerous problems, including that of exit burrs wedged between parts to be fastened, can be avoided by aligning and clamping the parts together prior to drilling. However, this principle has not been applied to the fastening of a nutplate to a workpiece in an automatic riveting machine.
The ITC attachment may occasionally damage the workpiece. A nutplate may lodge in the catching chamber in a "tipped" or cocked position. The workpiece may be fractured or dented when the lower ram presses the tipped nutplate against the workpiece lower surface. The catching chamber of the ITC nutplate attachment completely encloses the nutplate, preventing an operator from noticing the tipped condition of the nutplate and correcting it.
An automatic nutplate installation device that can install nutplates on curved or irregular assemblies would greatly increase manufacturing efficiency. In addition, such a device should precisely locate and align the nutplate in its intended position throughout the fastening machine cycle and in full view of the operator.
These problems and deficiencies are clearly felt in the art and are solved by the present invention in the manner described below.